Research Interests
Our laboratory uses genetics and molecular biology to study pattern formation in the early zebrafish embryo. The rapid development and simple anatomy of this teleost embryo, together with recently developed techniques for reverse genetics and a nearly complete genome sequence, make zebrafish a powerful molecular genetic system for studying the mechanisms of development. We focus on two areas: (i) neural crest specification and formation of the skeleton in the early embryo and (ii) long-range signals, morphogens, that pattern the anterior-posterior (A-P) axis of the nervous system. In both cases, we are interested in how gene functions translate into cell behaviours and the formation of tissues and organs.
A major focus of the work in our laboratory is to define as fully as possible the genetic and molecular pathways that establish the neural crest and its derivatives. Neural crest is a population of highly migratory cells that arise from the crests of the forming neural tube as it folds, and give rise to all of the body’s pigmentation, most of its peripheral nervous system, as well as the head skeleton. We have been analyzing and cloning the genes underlying a large library of mutations identified by their defects in the craniofacial skeleton. We have found that many of them disrupt genes involved in early specification of the neural crest. We recently showed requirements for several members of the activator protein-2 (ap-2) family of transcription factors in neural crest (Knight et al., 2005; Hoffman et al., 2007). We have also identified downstream targets that we now believe control neural crest migration, and these share many similarities with other migrating cell types, such as metastatic cancer cells.
Analysis of zebrafish mutants has also revealed signals that act on neural crest later as they assemble the craniofacial skeleton. We have shown that both Endothelin-1 signaling as well as the Atrophin-2 transcription factor are required to form joints in the craniofacial skeleton (Nair et al., 2007; Plaster et al., 2007). Endothelin-1 is required to specify the dorsal-ventral axis of the developing jaw.
A second, more recent focus of our lab is to understand the genetic and molecular pathways that specify the identities of cells along the A-P axis in the early embryo. Here we have begun to take a more computational, systems approach. The vitamin A derivative, retinoic acid (RA), is thought to be a diffusible factor that promotes posterior development. We initially showed that zebrafish mutants in an enzyme that synthesizes RA, called Retinaldehyde dehydrogenase (Raldh2), have defects in the formation of segments in the hindbrain, known as rhombomeres, that each contain unique sets of interneurons and motor neurons. More recently, my lab has studied requirements for: 1) other Raldh enzymes, 2) RA receptors (RARs), 3) cellular RA binding proteins (CRABPs), and 4) RA degrading enzymes (Cyp26s), in signaling. With RAR antagonists we defined separate critical periods for RA signaling in A-P patterning and neuronal differentiation in the hindbrain (Linville et al., 2004), as well as for pancreas development (Stafford et al., 2006). We have shown how each of these components influences cellular responses to RA as well as the distribution of RA itself through feedback, and Cyp26a1 plays a key role (White et al., 2007).
Linville A, Gumusaneli E, Chandraratna R and Schilling TF (2004). Independent roles for retinoic acid in segmentation and neuronal differentiation in the zebrafish hindbrain. Developmental Biology 270, 186-199.
Knight RD, Javidan Y, Zhang T, Nelson S and Schilling TF (2005). AP2-dependent signals from the ectoderm regulate craniofacial development in the zebrafish embryo. Development 132, 3127-3138.
Holzschuh J, Wada N, Wada C, Schaffer A, Javidan Y, Tallafuss A, Bally-Cuif L and Schilling TF (2005). Requirements for endoderm and BMP signaling in sensory neurogenesis in zebrafish. Development 132, 3731-3742.
Wada N, Javidan Y, Nelson S, Carney TJ, Kelsh RN and Schilling TF (2005). Hedgehog signaling is required for cranial neural crest morphogenesis and chondrogenesis at the midline in the zebrafish skull. Development 132, 3977-3988.
Stafford D, White R, Kinkel MD, Linville A, Schilling TF and Prince V (2006). Retinoids signal directly to zebrafish endoderm to specify insulin-expressing beta-cells. Development 133, 949-956.
Nair S, Wei J, Cornell R and Schilling TF (2007). Requirements for Endothelin receptors and Endothelin-1 signals from facial ectoderm in patterning skeletogenic neural crest in zebrafish. Development 134, 335-345.
Plaster N, Sonntag C, Schilling TF and Hammerschmidt M (2007). Atrophin-2 interacts with Fgf8 signaling in a histone-acetylase dependent manner. Developmental Dynamics, 236, 1891-1904.
Hoffman TF, Javier A, Campeau S, Knight RD and Schilling TF (2007). AP2 transcription factors in zebrafish development and vertebrate evolution. J Exp Zool, Mol Dev Evol 308B: 679-691.
White RJ, Nie Q, Lander AD, Schilling TF (2007) Complex regulation of cyp26a1 creates a robust retinoic acid gradient in the zebrafish embryo. PLoS Biol 5(11): e304. doi:10.1371/journal.pbio.0050304.